1. Field of the Invention
The present invention is related to engine cooling systems. More particularly, the present invention is directed to an engine cooling system particularly suited for incorporation in a small watercraft.
2. Description of the Related Art
Personal watercraft, like other applications that use internal combustion engines for propulsion, are experiencing considerable public and governmental pressure to improve not only their performance, but also their exhaust emissions level. For example, due at least in part to the emissions generated by two-stroke powered watercraft, certain recreational areas have banned the operation of such watercraft. These bans have decreased the popularity of personal watercraft, and have caused manufacturers of these types of watercraft to consider replacing conventional two-stroke type internal combustion engines with four-stroke engines to power the watercraft and/or other means to reduce emissions levels.
Although typical four-stroke type engines inherently produce less exhaust emissions than similar two-stroke engines, it nonetheless remains important to maintain the operating temperature of the four-stroke engine within a particular temperature range in order to fully realize the reduced emissions levels. For this purpose, a temperature-actuated valve, or a thermostat, is typically employed within the cooling system of the watercraft to maintain the desired operating temperature of the engine.
However, the thermostat is typically located downstream from the engine. Because the cooling water is typically supplied by the jet pump unit of the watercraft, the temperature of the cooling water supplied to the cooling system may over-cool the engine if the watercraft is operating in a body of water below a certain temperature. In an effort to solve this problem, some marine engines route the cooling water through a portion of the exhaust system before delivering it to the engine.
One aspect of the present invention is the realization that although it is preferable to route the cooling water through an exhaust manifold portion of the exhaust system, such a coolant flow-path may lead to drainage problems of the cooling system when the watercraft engine has been shutdown. For example, certain cooling jackets may not drain when the engine has been stopped, because of their position relative to other cooling system components. The drainage problem may result from the exhaust manifold being positioned above an inlet to the water jacket of the engine. Accordingly, in a preferred embodiment, the cooling system includes a separate drain passage in communication with the water jacket of the engine. The drain passage is configured to drain water from the water jacket of the engine so that the coolant supply passage may be routed through vertically higher components of the exhaust system, such as the exhaust manifold, without jeopardizing the draining of the cooling system when the engine is not running.
Accordingly, one aspect of the present invention involves a small watercraft comprising a hull defining an engine compartment. An internal combustion engine is supported within the engine compartment and drives a propulsion device. The engine has an engine body defining a cylinder and a cooling jacket at least partially surrounding the cylinder. A cooling system is in fluid communication with the cooling jacket and supplies cooling fluid to the cooling jacket through a supply passage. A portion of the supply passage is above a portion of the cooling jacket and a drain passage communicates with a lower portion of the cooling jacket. The drain passage is configured to drain cooling fluid from the cooling jacket.
Another aspect of the present invention involves a method of draining cooling fluid from a small watercraft engine having a cooling jacket at least partially surrounding a cylinder of the engine. The method comprises supplying the cooling fluid to the engine through a supply passage. The method further includes routing the supply passage into thermal communication with an exhaust manifold of the engine at a height above a portion of the cooling jacket and routing the supply passage into fluid communication with the cooling jacket to supply the cooling fluid to the cooling jacket and cool the engine while it is running. The method also includes allowing the cooling fluid to drain from a lower portion of the cooling jacket through a drain passage after the engine has stopped running.
Yet another aspect of the present invention involves a marine engine comprising an engine body defining a cylinder and a cooling jacket at least partially surrounding the cylinder. A cooling system is in fluid communication with the cooling jacket and supplies cooling fluid to the cooling jacket through a supply passage. A portion of the supply passage is above a portion of the cooling jacket. A drain passage communicates with a lower portion of the cooling jacket, the drain passage being configured to drain cooling fluid from the cooling jacket.